Cooling device with controllable evaporation temperature

ABSTRACT

A cooling device for cooling a test sample has at least two cascade cooling stages, each with at least one coolant line, one compressor ( 1.1, 2.1 ), one relief throttle ( 1.5 ), one evaporator ( 6, 7 ) and one liquefier ( 3, 6 ). The coolant line is divided into n partial lines (A, B) between the compressor ( 2.1 ) and the liquefier ( 6 ) of the last cascade cooling stage, wherein n≧2. Each divided n partial line (A, B) has a valve ( 2.7, 2.8 ) and an individual relief throttle ( 2.5, 2.6 ). The divided partial lines (A, B) are connected to the evaporator ( 7 ) of the last cascade cooling stage. This represents a simple possibility of adjusting the cooling temperature without using valves that must be adjusted in a cold state, since such valves are complex and expensive.

This application claims Paris Convention priority of DE 10 2011 006 174.6 filed Mar. 25, 2011 the complete disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention concerns a cooling device for cooling a test sample, comprising at least two cascade cooling stages, each comprising at least one coolant line, one compressor, one relief throttle, one evaporator and one liquefier.

Devices having such properties are e.g. the device NMR90 of the company Millrock Technology, Kingston, N.Y., USA, the device ULSP90 of the company ULSP bv, Ede, NL and the device FTS XR Air Jet of the company RototecSpintec GmbH, Biebesheim, Germany.

Various analysis methods require cooling of the samples to be analyzed. In specific cases, such as nuclear magnetic resonance spectroscopy or X-ray crystallography, this is often achieved by introducing the sample into a cold gas flow, advantageously nitrogen or helium.

This cold gas flow may be realized e.g. through evaporation of liquid gases or cooling a warm gas using heat exchangers that are immersed into liquefied gas. Provision or generation and storage of these liquefied gases requires complex logistics.

The warm gas may alternatively also be cooled using a coolant cycle process. In a cycle process, a suitable coolant is compressed in a compressor to a higher pressure and is thereby heated, then cooled (desuperheated) in a heat exchanger to a temperature below the liquefaction temperature that prevails at the obtained pressure, thereby dissipating heat, is further liquefied, thereby dissipating further heat, is relieved by a suitable throttle to a lower pressure, and evaporated again in a second heat exchanger, thereby absorbing heat from the gas to be cooled at the low evaporation temperature.

There are conventional configurations of coolant cycle processes with adjustable evaporation pressure and adjustable throttle between the first heat exchanger (coolant liquefier) and second heat exchanger (coolant evaporator) in order to adjust the desired cooling temperature. Such a configuration is technically complex when the cycle process to be varied is already operated in a cascade of cycle processes at a very low liquefaction temperature and the adjustable throttle consequently also becomes very cold.

For this reason, it is current practice to largely do without adjustment of the desired coolant temperature. This applies to the devices of the companies Bruker (type “BCU-X”), ULSP type “90 Immersion Probe Cooler”, and Milrock type “NMR90 sample cooler”. In an alternative fashion, the gas flow that has been cooled to a predetermined temperature is heated to a desired higher temperature by means of an installed heating device. One example therefore are the devices of the company RototecSpintec FTS “XR Air-Jet Cooler”.

It is the underlying purpose of the present invention to provide a simple way of adjusting the cooling temperature without using valves that must be adjusted in a cold state, since these are complex and expensive.

SUMMARY OF THE INVENTION

This object is achieved in a surprisingly simple and yet effective fashion in that the coolant line is divided into n partial lines between the compressor and the liquefier of the last cascade cooling stage, wherein n≧2, the divided n partial lines can be blocked individually and independently of each other by means of at least n−1 valves, the divided partial lines each comprise their own relief throttle, and the divided partial lines are both connected to the evaporator of the last cascade cooling stage.

In the inventive cooling device, the compressed coolant is divided into two or more parallel paths upstream of the first heat exchanger (liquefier) and guided in this fashion through the liquefier, through a separate respective throttle and to the second heat exchanger (evaporator). When the individual paths are selectively individually blocked by the valves thereof, one obtains an overall adjustable throttle effect. 2^(n−)1 different throttle effects can be adjusted for n valves when the individual throttles are properly dimensioned. At least one valve has to be open at any time, and for this reason, one valve can be omitted. One then obtains 2^(n) different throttle effects with n valves and n+1 coolant paths with each throttle. The coolant is evaporated, thereby providing the desired cooling power in the second heat exchanger at the evaporation temperature of the coolant at this influenceable pressure, and for this reason, the cooling temperature can also be influenced.

In contrast to the conventional devices, the throttles of this device need not be adjustable themselves, which could be realized only with great technical expense in a cascade of cycle processes of a cycle process to be varied with a very low liquefying temperature and therefore low throttle temperature.

One particularly preferred embodiment of the inventive cooling device is characterized in that the divided partial lines are guided in parallel through the liquefier.

One further advantageous embodiment is characterized in that the evaporator of the last cascade cooling stage is designed as a heat exchanger, a gas to be cooled enters the heat exchanger through a gas inlet, dissipates heat and exits the heat exchanger again through a gas outlet, and the cooled cooling gas is guided to the test sample for cooling it. With this design, the heat exchanger is simultaneously the transfer line for the cooling gas and the device can be designed in a simple and space-saving fashion.

The invention is particularly advantageous when the cooling device is part of a nuclear magnetic resonance spectroscopy apparatus, in which the cooled gas flow is heated to the desired temperature and higher temperatures can be achieved with less cooling and therefore also less heating, which simplifies control.

The inventive cooling device may alternatively also be part of an X-ray spectroscopy apparatus. In particular, X-ray crystallography often requires cooling of the test samples.

The inventive cooling device is alternatively also advantageously part of an EPR apparatus.

Further advantages of the invention can be extracted from the description and the drawing. The features mentioned above and below may be used individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but have exemplary character for describing the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic view of an embodiment of the inventive cooling device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The cooling device shown by way of example in FIG. 1 includes a first cascade cooling stage with compressor 1.1, safety pressure switch 1.2, filter 1.3, relief throttle 1.5, and pressure compensating vessel 1.4, and also a second cascade cooling stage with compressor 2.1, safety pressure switch 2.2, filter 2.3, and pressure compensating vessel 2.5.

A combined air heat exchanger with fan 5 is e.g. used as liquefier 3 for the first cascade cooling stage and as desuperheater 4 for the second cascade cooling stage.

A heat exchanger 6 is used as evaporator for the first cascade cooling stage and as liquefier for the second cascade cooling stage.

A heat exchanger 7, illustrated by way of example as transfer line, is used as evaporator for the second cascade cooling stage to provide the desired cooling power in that a gas to be cooled is guided from the inlet 7.1 to the outlet 7.2.

Downstream of the compressor 2.1 of the second cascade cooling stage, the coolant line of the illustrated embodiment is divided into two partial lines A, B. These are guided in parallel through the heat exchanger 6 downstream of the respective valves 2.7, 2.8. Each of the partial lines A, B, has its own relief throttle 2.5, 2.6. The two partial lines A, B, are subsequently guided into the heat exchanger 7. The evaporation temperature can then be controlled via connecting or disconnecting a partial line A, B, by means of the valves 2.7, 2.8.

Although the invention is illustrated above by means of a cooling device in accordance with the principle of a compression cooling machine with two-stage cooling cascade, adjustment of the evaporation temperature by dividing the coolant path upstream of the first heat exchanger into two or more paths is also possible with one-stage cooling devices according to this principle and also with cooling cascades with more than two stages.

List of Reference Numerals

-   1.1 compressor of the first cascade cooling stage -   1.2 safety pressure switch thereof -   1.3 filter thereof -   1.4 compensating vessel thereof -   1.5 relief throttle thereof -   2.1 compressor of the second cascade cooling stage -   2.2 safety pressure switch thereof -   2.3 filter thereof -   2.4 compensating vessel thereof -   2.5 relief throttle A thereof -   2.6 relief throttle B thereof -   2.7 valve to the relief throttle A thereof -   2.8 valve to the relief throttle B thereof -   3 liquefier of the first cascade cooling stage -   4 desuperheater of the second cascade cooling stage -   5 fan for liquefier 3 and desupercooler 4 -   6 heat exchanger as evaporator of the first cascade cooling stage     and liquefier of the second cascade cooling stage -   7 heat exchanger as evaporator of the second cascade cooling stage     for providing the cooling power by cooling a gas -   7.1 entry of the gas to be cooled -   7.2 exit of the cooled gas 

1. A cooling device for cooling a test sample, the cooling device comprising: at least one first cascade non-final cooling stage, said first non-final cooling stage having at least one first coolant line, a first compressor, a first relief throttle, a first evaporator and a first liquefier; and a second final cascade cooling stage, said second final cascade cooling stage having at least one second coolant line, a second compressor, a second relief throttle, a second evaporator and a second liquefier, said second coolant line being divided into n partial lines between said second compressor and said second liquefier, wherein n≧2, said divided n partial lines structured for individual blockage thereof and independently of an other by means of at least n−1 valves, each divided partial line having an individual relief throttle, wherein said divided partial lines are connected to said second evaporator.
 2. The cooling device of claim 1, wherein said divided partial lines are guided in parallel through said second liquefier.
 3. The cooling device of claim 1, wherein said second evaporator is designed as a heat exchanger, a gas to be cooled entering said heat exchanger through a gas inlet, dissipates heat, exits said heat exchanger again through a gas outlet and is guided to the test sample for cooling thereof.
 4. The cooling device of claim 1, wherein the cooling device is structured for use in a nuclear magnetic resonance spectroscopy apparatus.
 5. The cooling device of claim 1, wherein the cooling device is structured for use in an X-ray spectroscopy apparatus.
 6. The cooling device of claim 1, wherein the cooling device is structured for use in an EPR apparatus. 